Electronic printing press
An electronic printer comprising a source of charged toner particles, a writing head capable of imaging individual toner particles, means to transfer the toner image to a print substrate, and a fuser. The writing head employs toner conveyors driven by voltage traveling waves. Imaging is achieved using a diverter electrode in each toner conveyor, and diverted toner is returned to the toner source. High speed is achieved using a plurality of independent toner conveyors that operate in parallel. A printing press capable of printing variable images at 200 feet per minute with a print width of 48 inches and a print resolution of 2,400 dots per inch is described.
This invention relates to printers and more particularly to an electronic method of variable printing at high resolution and high speed.
DESCRIPTION OF THE RELATED ARTThe fastest and highest quality printers or printing presses of today utilize offset printing or photogravure methods. With photogravure, an imaging drum is photolithographically patterned. With offset printing, image data is typically patterned on a plate. Using either method, the patterned surface is inked with a printing paste, and the paste image is transferred to a print substrate at high speed, in a repeating cycle. Thereby, multiple copies of the image data are created on the print substrate or medium. The print medium may be in the form of a web such as a continuous roll of paper, with the printed web being subsequently converted into printed sheets. The print substrate or medium can also be in sheet form. Photogravure printers can operate at web speeds of several hundred feet per minute, with typical print resolutions of 2,400 dots per inch. Their image quality is currently the best available among printers of all types. However, economical run lengths are typically around ten thousand printed pages because of substantial setup procedures and “make ready” costs for each printing run.
Modern commerce utilizes imagery in advertisements and brochures that often require up-to-date information. The information can change daily or even hourly. Thus a new type of printing has emerged, called “variable printing”, or “printing on demand”. Variable printers support short run lengths, typically a few hundred pages. They generally employ electronic printing methods, without requiring permanently patterned plates or drums. One such electronic method is the laser printing method, wherein a latent toner image is formed on a charged photoconductive drum by modulating light from a scanning laser beam. Where the surface of the photoconductive drum is illuminated by the spot of the laser beam, it is discharged. The resulting latent image is developed by flowing charged toner over the drum, to form a toner image. The toner image is typically transferred to a roll or belt and from there to a print substrate where it is fused to form a permanent image. For high speed printers, the laser printing process is limited by the serial nature of the laser scan; each laser beam can image only one pixel at a time. One pixel corresponds to one spot or one dot on the printed page.
Chemical toners or polymerized toners are created by growing toner particles out of a liquid bath. The prior method of toner manufacture involved grinding of plastic material, and sieving to classify particle size. This produced “attrited toner” which was characterized by irregularly shaped particles. By contrast, chemical toners produce particles with uniform size and shape. Of the available shapes, spherical particles are the simplest and easiest to produce. Although more primary colors are sometimes used, cyan, magenta, yellow, and black (CMYK) form a typical set of primary colors. A full gamut of printed colors can be created by overlaying measured amounts of the primary colors. Translucent toner particles typically provide the best color quality in overlaid images of this type.
Flat panel displays (FPDs) are currently being manufactured on glass panels as large as 2160 mm by 2400 mm, with feature sizes (line width and space) smaller than 1 μm. By comparison, the writing head of the preferred embodiment of the current invention requires a feature size of around 1.8 μm and a width dimension of around 50 inches or 1270 mm.
The following related patents are hereby incorporated by reference in their entirety for their teachings:
U.S. Pat. No. 5,153,617 to Peter C. Salmon, issued Oct. 6, 1992, for “Digitally Controlled Method and Apparatus for Delivering Toners to Substrates”.
U.S. Pat. No. 5,400,062 to Peter C. Salmon, issued Mar. 21, 1995, for “Electrostatic Printing Apparatus and Method”.
U.S. Pat. No. 6,309,049 to Peter C. Salmon, issued Oct. 30, 2001, for “Printing Apparatus and Method for Imaging Charged Toner Particles Using Direct Writing Methods”.
In particular, these patents teach the use of particle conveyors employing voltage traveling waves (617); digitally controlled toner conveyors (062); and polymerized toners and diverter electrodes (049).
SUMMARY OF THE INVENTIONAn electronic printing method is described for printing variable images at rates of several hundred feet per minute, with a print width of 48 inches and a print resolution of 2,400 dots per inch. A dry toner is employed and each particle is electrostatically charged. The imaging method employs voltage traveling waves applied to toner conveyors arrayed in columns, each column imaging toner for delivery to one pixel on the printed page. The toner is imaged using diverter electrodes, and each toner particle is individually controlled and imaged in the preferred embodiment. For color printing, a separate print engine is provided for each primary color, and the print engines are arranged in series. Thus, the primary colors are super-imposed to create the hues of the final image.
The accompanying drawings, which are somewhat schematic in some instances and are incorporated in and form a part of this specification, illustrate a primary embodiment of the invention and, together with the description, serve to explain the principles of the invention.
Various embodiments of the present invention are described hereinafter with reference to the figures. It should also be noted that the figures are only intended to facilitate the description of specific embodiments of the invention. They are not intended as an exhaustive description of the invention or as a limitation on the scope of the invention. In addition, an aspect described in conjunction with a particular embodiment of the present invention is not necessarily limited to that embodiment and can be practiced in any other embodiments. For instance, the preferred embodiment describes a high-end printer with resolution of around 2,400 dpi. Lower resolution printers may have adequate quality for many applications and may be manufacturable at lower cost. Such lower resolution printers may use wider conveyors that image toner in groups of multiple particles rather than one particle at a time, yet the same imaging principles will apply. The imaging method of the current invention may also be employed with different supporting apparatus and methods. For example, toner particle charging may utilize a fluidized bed, as is known in the art; in this case toner charging will occur externally to the toner hopper. Different methods may be used for transferring the toner image or fusing it. For example a transfix process could be employed, or a radiant fuser. Additionally, other embodiments and applications will be apparent to those who are skilled in the art.
Since toner particles may cycle through the imaging process several times, depending on how many times they are ejected by a diverter electrode, the toner used in the current invention is preferably a “robust toner”. It will retain its physical size and shape as well as its charge characteristics, even as it is “worked” in the print engine. The preferred spherical shape of the toner supports this type of robustness. In addition, the writing head is preferably coated with a material that is tribo-electrically matched to the toner, to improve the tribo-electric environment for particles moving on the conveyors. Each contact of a charged particle with another particle or surface is a potential charging or discharging event. By coating the control surfaces (e.g., toner conveyors) with either the constituent materials of the toner particles or material equivalents having similar tribo-electric properties, the surfaces will behave like the surface of a toner particle, with respect to contact charging events. This is desirable because the toner particles are designed to collide and physically interact with each other without significantly charging or discharging one another. Neutral charging behavior of control surfaces should be optimized after a short period of operation, wherein the toner conveyors become coated with a distribution of flow control particles and charge control agents (additive particles) that came from interaction with the toner particles. The preferred steady state condition is that this distribution of additive particles remains approximately constant on the toner conveyor surfaces, resulting in an approximately constant distribution of charge on the toner particles as they move throughout the print engine. To implement this strategy, actual toner particles used in the print engine may be dissolved in toluene or other suitable solvent, creating a fluid that can be painted or sprayed on the conveyors to achieve a coating with the desired charging neutrality. Alternatively, the toner constituent materials or material equivalents, including one or more base polymers, flow control additives, charge control agents, and optionally the colorants, can be combined using a solvent to form a solution for coating the writing heads.
The resulting structure is shown in
The advantages of the preferred embodiment of the current invention relate primarily to print speed, print resolution, cost of manufacture of the print system, and short run economy for variable printing as measured by the cost per page. As described, the preferred resolution is 2,400 DPI, and this is achieved by individually controlling each toner particle. Other electronic printers have not achieved to date this fine control over individual toner particles. While delivering this fine-grained image quality, the preferred speed of the 48-inch wide preferred print substrate is 200 feet per minute, at the upper end of speeds available from printing presses of all types. This high performance is achievable because a modern printer controller augmented by IC chips on the writing head is fast enough to process the print data and distribute the required control signals, and because the imaging process is highly parallel. The parallel process of the current invention contrasts with electrophotography (Xerography) wherein a scanning laser is used to sequentially form the image. At the preferred resolution and speed, there are 115,200 independent single-particle-print-engines (micro print engines), each contributing an imaging event every 10 microseconds. Each micro-print engine includes a toner conveyor equipped with a diverter electrode and a transfer electrode. The imaging power of the print system described sums to over 10 billion (1.15×1010) individual toner particles imaged per second. Moreover, every page can portray different print data (variable printing), resulting in an economical run length of just a few pages. Another cost factor for electrophotographic printing surrounds the use of photoconductive drums; these have a maintenance life of a few thousand pages. This cost is eliminated using the solid state printing process of the current invention, wherein the print algorithm is implemented using an array of special purpose IC chips mounted on the writing head, supported by a fast general-purpose computer implementing the print controller. Many of the mechanical components of existing high-end print systems are replaced by electronic equivalents, and this can lead to highly reliable operation and low maintenance costs. The size, mass, and footprint of the preferred embodiment are each at least an order of magnitude less than their counterparts observed in printing presses operating today.
Claims
1. A printing method for use with a print substrate and a toner hopper containing toner particles comprising the steps of:
- charging the toner particles;
- loading the charged toner particles onto a writing head;
- providing on said writing head toner conveyors that are one toner particle wide; transporting the charged particles on the toner conveyors;
- selectively ejecting certain charged particles being transported on each toner conveyor to form a toner image from the remaining charged particles transported on the toner conveyor; and,
- transferring the toner image formed by each toner conveyor to a corresponding pixel site on the print substrate.
2. The printing method of claim 1 including the step of fusing the transferred toner image on the print substrate.
3. The printing method of claim 1 including the step of providing barrier electrodes at the longitudinal edges of each toner conveyor for containing the charged toner particles being transported.
4. The printing method of claim 1 including the step of feeding the print substrate as a continuous web during the transferring step.
5. The printing method of claim 1, including the step of returning the ejected particles to the toner hopper.
6. The printing method of claim 1 wherein the writing head includes a glass substrate.
7. The printing method of claim 1 wherein the conveying step includes providing voltage traveling waves.
8. The printing method of claim 1 wherein the step of selectively ejecting certain charged particles includes activating a diverter electrode in each of the toner conveyors to selectively eject the certain charged particles in accordance with the toner image.
9. The printing method of claim 3 wherein the barrier electrodes are spaced apart sufficiently to enable transport of a plurality of particles on each conveyor electrode of each toner conveyor.
10. The printing method of claim 8 wherein the step of activating a diverter electrode in each of the toner conveyors is controlled by a print controller that receives print data from an information source and generates control signals to integrated circuit chips mounted on the writing head, and the integrated circuit chips provide a control signal to each of the diverter electrodes.
11. A print system for use with a print substrate and toner particles comprising:
- a toner hopper adapted for containing the toner particles;
- a toner charging device for charging the toner particles;
- a writing head for receiving the charged toner particles from the toner charging device and transporting the charged toner particles on toner conveyors;
- barrier electrodes defining the width of each toner conveyor wherein the barrier electrodes are spaced apart by approximately one toner diameter;
- a diverter electrode in each toner conveyor for selectively ejecting certain charged toner particles from the toner conveyor to form a toner image from the charged toner particles remaining on the toner conveyor;
- a return conveyor for returning the ejected toner particles to the toner hopper; a transfer roll or belt for transferring the toner image to the print substrate; and, a controller that accepts print data delivered to the print system and controls the diverters in accordance with the toner image.
12. The print system of claim 11 including a fuser for fusing the transferred toner image on the print substrate.
13. The print system of claim 11 wherein the controller includes integrated circuit chips mounted on the writing head.
14. The print system of claim 11 wherein the toner conveyors employ voltage traveling waves.
15. The print system of claim 11 wherein the width of the toner conveyors and the width of the diverter electrodes is approximately one toner particle wide.
16. The print system of claim 11 wherein the width of the toner conveyors and the width of the diverter electrodes is several toner particles wide.
17. The print system of claim 11 wherein the writing head includes a glass substrate.
18. The print system of claim 11 wherein the writing head has a width of 8-50 inches.
19. The print system of claim 11 wherein the toner image has a resolution of 300-2,500 dots per inch.
20. The print system of claim 11 wherein at least eighty percent of the toner particles have a diameter within twenty percent of the mean toner particle diameter.
21. A print system comprising a plurality of print engines arranged serially about a print substrate, each engine corresponding to a primary color to be printed, wherein each print engine comprises:
- a section of the print substrate;
- a toner hopper;
- toner particles having a primary color in said hopper;
- a toner charging device for charging the toner particles;
- a writing head for accepting the charged toner particles and transporting them on toner conveyors;
- diverter electrodes in each of the toner conveyors for selectively ejecting certain ones of the charged toner particles to form a toner image from the remaining charged toner particles; a return toner conveyor for returning the ejected toner particles to the toner hopper; a transfer roll or belt for transferring the toner image from the conveyors on the writing head to the print substrate; and,
- a controller that accepts print data delivered to the print system and controls the diverters in accordance with the toner image.
22. The print system of claim 21 including one or more fusers for fusing on the print substrate images transferred from the print engines in said serial arrangement.
23. A method for providing matched tribo-electric properties within a printing system using toner particles and control surfaces comprising the step of:
- forming on the control surfaces a coating derived from the constituent materials of the toner particles, or derived from material equivalents of the constituent materials having similar triboelectric properties.
Type: Application
Filed: Aug 9, 2006
Publication Date: Feb 14, 2008
Inventor: Peter C. Salmon (Mountain View, CA)
Application Number: 11/502,223
International Classification: B41J 2/385 (20060101);